Economic evaluation of drug abuse treatment and HIV prevention services for pregnant women is critical to identify the most efficient and equitable use of scarce resources. Economic and policy research on the efficiency of drug abuse treatment and HIV prevention services among vulnerable populations such as women, adolescents and members of minority groups is necessary to improve drug abuse and HIV/AIDS services for these vulnerable and underserved populations. While work in this area continues to grow, there is still a dearth of rigorous economic evaluations of such programs, especially those that adhere to quality standards as recommended by the U.S. Panel on Cost Effectiveness in Health and Medicine. The overall objective of this study is to conduct the first economic evaluation of an innovative behavioral approach integrating Motivational Enhancement Therapy with Cognitive Behavioral Therapy (MET-CBT) as compared to standard Brief Advice (BA) within prenatal care to decrease use of a full range of substances (e.g., marijuana, cocaine, methamphetamines, alcohol, nicotine), to reduce HIV risk behavior and to achieve better infant health outcomes (e.g. longer gestations, greater birth weight, reduced medical consequences such as admission and length of stay in the Neonatal Intensive Care Unit (NICU)). The specific aims of this study are: (1) to conduct cost analyses of the MET-CBT and BA intervention arms; (2) to conduct incremental cost-effectiveness analyses of the two interventions (MET-CBT and BA), vis-`-vis each other, in terms of substance use, infant health outcomes and HIV risk reduction; and (3) to conduct incremental cost-utility analyses determining the net cost per Quality-Adjusted Life Year (QALY) saved respectively by each intervention arm (MET-CBT and BA), vis-`-vis each other, in terms of substance use and HIV risk reduction. The proposed research is responsive to PA-07-122 in that it proposes to conduct research related to cost-effectiveness and cost-utility analyses, services costs, methodological research, and the cross-cutting themes of HIV/AIDS and health disparities. The proposed research is grounded in sound microeconomic principles and standardized techniques as reported in the U.S. Panel on Cost Effectiveness in Health and Medicine, and proposes rigorous conceptual and methodological research to improve the evidence base on the unit costs and cost-effectiveness of substance abuse treatment and HIV prevention services. It builds on a NIDA-funded randomized controlled trial (R01-DA019135) of an innovate behavioral approach, which offers a new paradigm of treatment services, integrating MET-CBT within prenatal care compared to standard BA, and offering promise to improve access to and strengthen substance use treatment and HIV prevention services targeted at drug using pregnant women who are highly susceptible to HIV/AIDS.